The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A098685 Numbers n such that pi(n) = sigma(d_1)*sigma(d_2)*...*sigma(d_k) where d_1 d_2 ... d_k is the decimal expansion of n. 4
 15, 155, 252, 916, 1189, 12654, 55293, 177554, 418634, 753248, 885193, 18252678, 18252687, 18469156, 18469165, 19882616, 19882623, 41867246, 73526936, 73526957, 233843449, 244895519, 2345784285, 2399877831, 4273447776, 29891923496, 42649454852, 728781494646 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) must necessarily be a zeroless number. - Chai Wah Wu, Mar 04 2019 LINKS Chai Wah Wu, Table of n, a(n) for n = 1..34 EXAMPLE 885193 is in the sequence because pi(885193) = sigma(8)*sigma(8)*sigma(5)*sigma(1)*sigma(9)*sigma(3). MATHEMATICA Do[d=IntegerDigits[n]; k=Length[d]; If[ !MemberQ[d, 0]&&PrimePi[n]== Product[DivisorSigma[1, d[[j]]], {j, k}], Print[n]], {n, 10000000}] CROSSREFS Cf. A000203, A000720, A052382, A098686, A098683, A098684. Sequence in context: A017389 A278803 A157380 * A223995 A323971 A006096 Adjacent sequences:  A098682 A098683 A098684 * A098686 A098687 A098688 KEYWORD base,nonn AUTHOR Farideh Firoozbakht, Sep 24 2004 EXTENSIONS a(12)-a(25) from Donovan Johnson, Jun 18 2009 a(26)-a(28) from Chai Wah Wu, Mar 04 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 20 23:46 EDT 2021. Contains 343143 sequences. (Running on oeis4.)